每次構建后更改自定義ListView.Items

Question

我創建了一個自定義的ListView ，它繼承自.NET標准ListView ，以顯示enum值作為其Items （ WinForms項目）：

public class ScrapGroupsListView : ListView
{
    public event EventHandler SelectedColorChanged;

    private ScrapGroup _selectedGroup = ScrapGroup.None;

    [DefaultValue(ScrapGroup.None)]
    public ScrapGroup SelectedScrapGroup
    {
        get { return _selectedGroup; }
        set
        {
            if (_selectedGroup != value)
            {
                _selectedGroup = value;
                foreach (ListViewItem item in this.Items)
                {
                    if (item != null)
                    {
                        if (item.Tag != null)
                        {
                            var itemColor = (ScrapGroup)item.Tag;
                            if (itemColor == ScrapGroup.None) 
                                item.Checked = value == ScrapGroup.None;
                            else
                                item.Checked = value.HasFlag(itemColor);
                        }
                    }
                }

                if (SelectedColorChanged != null) 
                   SelectedColorChanged.Invoke(this, EventArgs.Empty);
            }
        }
    }

    public ScrapGroupsListView()
    {
        this.Items.Clear();
        this.CheckBoxes = true;
        this.HeaderStyle = ColumnHeaderStyle.None;
        this.View = View.List;

        foreach (var value in Enum.GetValues(typeof(ScrapGroup)).Cast<ScrapGroup>())
        {
            this.Items.Add(new ListViewItem()
            {
                Name = value.ToString(),
                Text = value.ToString(),
                Tag = value,
            });
        }
    }

    protected override void OnItemChecked(ItemCheckedEventArgs e)
    {
        base.OnItemChecked(e);

        var checkedScrapGroup = (ScrapGroup)e.Item.Tag;

        if (e.Item.Checked)
            if (checkedScrapGroup == ScrapGroup.None)
                SelectedScrapGroup = ScrapGroup.None;
            else
                SelectedScrapGroup |= checkedScrapGroup;
        else
            SelectedScrapGroup &= ~checkedScrapGroup;
    }
}

ScrapGrouop是我的枚舉：

[Flags]
public enum ScrapGroup
{
    None=0,
    M=1,
    E=2,
    N=4,
    H=8
}

當我把ScrapGroupsListView放到我的表單時，一切正常，控件沒有Items：

但是每次構建項目時， ScrapGroup值都會添加到ScrapGroupsListView.Items （設計時）：

第一次構建后：

第二次構建后：

等等。

問題出在哪兒？

Answer 1

而不是構造函數嘗試：

protected override void OnCreateControl()
    {
        base.OnCreateControl();

        this.Items.Clear();
        this.CheckBoxes = true;
        this.HeaderStyle = ColumnHeaderStyle.None;
        this.View = View.List;

        foreach (var value in Enum.GetValues(typeof(ScrapGroup)).Cast<ScrapGroup>())
        {
            this.Items.Add(new ListViewItem()
            {
                Name = value.ToString(),
                Text = value.ToString(),
                Tag = value,
            });
        }
    }

Answer 2

每次在VS設計器中打開表單時，它都會創建以下代碼：

private void InitializeComponent()
{
    System.Windows.Forms.ListViewItem listViewItem1 = new System.Windows.Forms.ListViewItem("None");
    System.Windows.Forms.ListViewItem listViewItem2 = new System.Windows.Forms.ListViewItem("M");
    System.Windows.Forms.ListViewItem listViewItem3 = new System.Windows.Forms.ListViewItem("E");
    System.Windows.Forms.ListViewItem listViewItem4 = new System.Windows.Forms.ListViewItem("N");
    System.Windows.Forms.ListViewItem listViewItem5 = new System.Windows.Forms.ListViewItem("H");
    this.scrapGroupsListView1 = new ScrapGroupsListView();
    // 
    // scrapGroupsListView1
    // 
    this.scrapGroupsListView1.CheckBoxes = true;
    this.scrapGroupsListView1.HeaderStyle = System.Windows.Forms.ColumnHeaderStyle.None;
    listViewItem1.StateImageIndex = 0;
    listViewItem1.Tag = ScrapGroup.None;
    listViewItem2.StateImageIndex = 0;
    listViewItem2.Tag = ScrapGroup.M;
    listViewItem3.StateImageIndex = 0;
    listViewItem3.Tag = ScrapGroup.E;
    listViewItem4.StateImageIndex = 0;
    listViewItem4.Tag = ScrapGroup.N;
    listViewItem5.StateImageIndex = 0;
    listViewItem5.Tag = ScrapGroup.H;
    this.scrapGroupsListView1.Items.AddRange(new System.Windows.Forms.ListViewItem[] {
    listViewItem1,
    listViewItem2,
    listViewItem3,
    listViewItem4,
    listViewItem5});

這就是您的商品出現兩次的原因。 首先從構造函數設置，第二個從InitializeComponent()設置。

您可以（並且應該）從InitializeComponent() ）中刪除代碼，但在設計器中打開表單會再次將其搞砸。

為了防止這種情況，您可以將填充代碼移動到單獨的方法並從表單中調用它。

在你的控制中：

public ScrapGroupsListView()
{
    this.CheckBoxes = true;
    this.HeaderStyle = ColumnHeaderStyle.None;
    this.View = View.List;
}

public void Fill()
{
    this.Items.Clear();

    foreach( var value in Enum.GetValues( typeof( ScrapGroup ) ).Cast<ScrapGroup>() )
    {
        this.Items.Add( new ListViewItem()
        {
            Name = value.ToString(),
            Text = value.ToString(),
            Tag = value,
        } );
    }
}

在你的形式：

public MainForm()
{
    InitializeComponent();

    scrapGroupsListView1.Fill();
}

作為此解決方案的缺點，您在設計器中看不到您的項目。